Method for agglomeration measuring and control

ABSTRACT

The apparatus extracts samples of a fluid stream containing colloidal suspended solids at a detection station wherein the electrophoretic mobility (EM) of the colloidal suspended solids is determined. The detection station automatically measures the EM and provides such data to a computer, which computes the Zeta Potential. The computer also receives other information relating to the characteristics of the colloidal suspended solids, such as temperature, the percent of solids, and the flow rate of the fluid system. The computer is programmed to interpret the input data and to provide corrective signals to processing apparatus which automatically adjust and control the additives fed into the fluid stream to achieve automatic flocculation correction so that the agglomeration of the colloidal suspended solids in the fluid stream is optimized.

United States Patent 1 Komline, Sr. et al.

[ 1 Mar. 27, 1973 154] METHOD FOR AGGLOMERATION MEASURING AND CONTROL[75] Inventors: Thomas R. Komllne, Sr., Gladstone; Walter R. Wills,Cedar Knolls, both [2]] Appl. No.: 188,516

3,572,930 3/1971 Morcom et al. ..73/6l .4 X

Primary ExaminerMalcolm A. Morrison Assistant ExaminerR. StephenDildine, Jr.

AttorneyWatson, Cole, Grindle & Watson [57] ABSTRACT The apparatusextracts samples of a fluid stream containing colloidal suspended solidsat a detection station wherein the electrophoretic mobility (EM) of thecolloidal suspended solids is determined. The detection stationautomatically measures the EM and pro- 52 us. Cl. ..235/15l.31, 73/614,204/149, vides Such data to a computer, which computes the 204/195 R,204/299, 210/85, 324/9 Zeta Potential. The computer also receives otherin- 324/109 formation relating to the characteristics of the col- 51 In.0 15 4 G01 21 2 o 33 loidal suspended SOIldS, such as temperature, theper- [58] Field ofSearch ..204/l80 B, 195 R, 195 B, cent of Solids, andthe flow rate f the fluid ys 204/95 |"299 149: 73/614; 210/85; 324/92The computer is programmed to Interpret the input 109:235H5L3, 151.31data and to provide corrective signals to processing apparatus whichautomatically adjust and control the additives fed into the fluid streamto achieve auto- [56] References Cited matic flocculation correction sothat the agglomera- UNITED STATES PATENTS tion of the colloidalsuspended solids in the fluid v stream is optimized. 3,394,310 7/l968Baker et al. ..324Il09 X 6 Claims, 2 Drawing Figures 38 PROPORTlONN. vLuag P COMPUTER CONTROLLER PROPOlZTlONN.

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SHEET 1 [If 2 PROPORTlONAL 3e PLUS RESET 2mm coMPuTEQ CONTROLLER \ePROPORTDNN.

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v' v E,

ELECTROPHOREStS .8 f: v CELL mscmzes I 1 ciN 8614 V WATER FLUSH T0SETTUNG m 0R FLowmN aquwmam' \9 55 FLOW we RAW SEWAGE OR AQTWATED SLUDGEPATENTEDHARZYIBYS 2 ,712

SHEET 2 OF 2 TELEV\S\ON MON\TOR\ \e, gcggxs; COMPUTER CELL To VOLTAGECASCADE METER ROLLER 4o V\D\CON SCANNER ELECTROPHORESB CELL METHOD FORAGGLOMERATION MEASURING AND CONTROL This invention relates to methodsfor optimizing conglomeration of any fluid stream containing colloidalsuspended solids and, more particularly, to a method determining theZeta Potential of colloidal suspended solids from their electrophoreticmobility and a method for the continuous analysis and selection ofcorrection measures in accordance with the Zeta Potential toautomatically control and select the additives fed into the process orstream to achieve an optimized agglomeration.

The method of the invention determines the Zeta Potential of colloidalsuspended particles or aggregates of colloidal suspended particles in afluid stream. The diameter of the particles and aggregates of interestis, in most cases, in the range of one to 50 microns. It is well knownthat particles of activated sludge or untreated, raw sewage possess anelectric charge that can be accurately determined in an electrophoresiscell. It is also recognized that the mechanics of measurement forconcentrated suspensions differ somewhat from the standard methodsemployed for the measurement of Zeta Potential of dilute colloidalsuspensions. That is, if a sludge is too dense to be viewed optically inan electrophoresis cell, it may be necessary to treat the sludge in someway to make it less dense so that optical detection of the particles ispossible.

A dense sludge can be viewed optically by first separating the liquidphase from the solid and then returning a small portion of the solid toa large portion of the liquid to give a suspended solids concentrationof about 100 parts per million. The liquid-solids separation may beachieved by filtration, centrifugation, or any other method which doesnot alter the electrolytic composition of the liquid phase. Simpledilution with water from another source in most cases changes theelectrolytic balance and as a result the Zeta Potential is also changed.

The invention provides methods for sampling any fluid stream containingcolloidal suspended solids and detecting the electrophoretic mobility ofthe suspended solids. Information relating to the motion of thesuspended particles is converted into electrical signals and fed to asuitably programmed computer which determines the velocity of theparticles, and in conjunction with other information relating to thecharacteristics of the suspended solids, such as the percentage ofsludge and the rate of flow of the fluid stream, generates appropriatecontrol signals which are then fed to corrective apparatus for alteringthe addition of additives into the process or stream to optimize theagglomeration of the colloidal suspended solids. The

methods disclosed herein are particularly suitable for water and sewagetreatment plants, industrial waste treatment, industrial solids recoveryand/or other industrial process applications.

OBJECTS It is a primary object of this invention to provide methods forthe automatic optimization of agglomeration or stabilization in anyfluid stream containing colloidal suspended solids.

It is a second object of this invention to provide methods forautomatically determining the Zeta Potential of suspended solids in afluid stream from a determination of the electrophoretic mobility of thesuspended solids.

A third object of the invention is to provide greatly improved methodsfor automatically determining the electrophoretic mobility of colloidalsuspended solids in any fluid stream.

A fourth object of the invention is to provide improved automatic andmore versatile control of the agglomeration or, stabilization of anyfluid stream containing colloidal suspended solids.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1a is a combined block anddiagrammatic illustration of an embodiment of a measuring andagglomeration control system in accordance with the invention; and

FIG. lb illustrates a preferred embodiment of the control systemdisclosed in FIG. la.

DETAILED DESCRIPTION OF THE INVENTION Influent (sludge) is pumped intoflocculation tank 10 where it is treated by suitable flocculents fromflocculent storage tanks 12 by means of flocculent feed pumps 14 whichare controlled by computer signals on line 16 to alter the flocculentpumped into the flocculation tank. The conditioned sludge is pumped fromflocculation tank 10 via sampling port 20 to be pumped intoelectrophoresis cell 22. The unsampled sludge is pumped to settling orflotation equipment (not shown). Provision is made for diluting sludgefrom flocculation tank 10 with water to improve the optical density ofthe sludge so that the colloidal suspended solids therein may beoptically viewed or tracked in electrophoresis cell 22. For this purposeas well as to purge the electrophoresis cell, clean water flush 24 isprovided.

Lens system 28 magnifies the colloidal motion sufficiently so as toproduce an image which is scanned by an electro-optical scanner ortracker 32. Scanner 32 is essentially a photomultiplier tube with servocircuitry for locking onto and tracking a dark or a light spot andproviding displacement data thereof in both X and Y- directions. Thedisplacement data is converted by velocity module 34 into rate ofdisplacement and produces signals proportional to dx/dt and dy/dt. Therate of displacement data in turn is fed to programmed computer 36 andcombined with the voltage of electrophoresis cell 22 and sampletemperature data respectively from cell voltage module 34a andtemperature module 34b to compute the Zeta Potential. A waste streamflow rate signal is fed from flow rate sensor 35 to proportional plusreset ratio controller 38 which delivers a signal to proportional plusreset cascade controller 40. The Z? signal from computer 36 is also fedto'cascade controller 40 and the resultant control signal regulates thespeed of pumps 14 by means of pump controls 39.

Scanner 32 may comprise a series 800 Electro-Optical Motion tracker asmanufactured by the Optron Corporation. Electrophoresis cell 22 ispositioned on the stage of a microscope and the optical head of thetracker is positioned to receive the magnified image. The output oftracker 32 is an analog voltage of i 5 volts and is proportional to thedisplacement of a tracked object or objects along the X or Y-axis, orboth axes simultaneously. Velocity module 34 may simply comprise adifferentiating circuit to generate a signal representing thedifferentiation of the tracker output voltage. The differentiatedsignals are stored in computer 36. The computer calculates an averagevelocity from the stored data and then calculates the corresponding ZetaPotential from an equation described below.

FIG. lb illustrates a preferred embodiment of scanning and trackerapparatus 32 for measuring the velocity of particle migration within theelectrophoresis cell. In this embodiment the scanner comprises the 1rMCparticle measurement computer manufactured my Millipore, a subsidiary ofBausch and Lomb. As in the aforedescribed embodiment, electrophoresiscell 22 is placed on the stage of a microscope 28 and the magnifiedimage is scanned by video scanner 44, which is part of the rrMC system.A computer associated with video scanner 44 identifies each particle andlocates its position from the coordinates of the tangent of the lowerportion of the particle. The particle location coordinates are stored incomputer 36. An average velocity determination is made by determiningthe total distance travelled by the particles divided by the totalnumber of particles divided by the time interval between observations.The computer associated with video scanner 44 already has the capabilityof performing division and multiplication. Therefore, it can beprogrammed to determine particle velocity and supply such data tocomputer 36 wherein the Zeta Potential for the suspended particles iscalculated. The flow rate and Zeta Potential signals are processed bycontrollers 38 and 40 as in FIG. la to produce control signals for pumps14.

THE DERIVATION OF THE WORKING EQUATIONS FOR DETERMINING ZETA POTENTIALThe classical expression for electroosmotic velocity of a fluid causedby a voltage gradient is:

where: v, electroosmotic velocity, D dielectric constant of the medium,E electric field strength, ZP zeta potential, n viscosity of the medium.The above equation can be used to determine Zeta Potential by rewritingit as follows:

In this equation E, the field strength, is replaced by V/L, the voltagedivided by the distance between the electrodes. In all our work we havetaken 22.5 C as our reference temperature and all Zeta Potentialmeasurements are corrected to 225. In this way the ZP equation becomes:

where n is the viscosity at 22.5 and c is a correction factor for thechange of viscosity with temperature. Now the equation is in a form thatcan be used by a computer to automatically determine ZP on the basis ofthree input signals, particle velocity (electroosmotic velocity), cellvoltage, and temperature. In the case of the first embodiment, theparticle velocity signal will be analog and proportional to velocity sothe basic ZP equation will be:

where: K 4'n'Ln/D, so K is a function of the cell dimensions and thetime and distance units used in the equation.

With the second and preferred embodiment, there are two choices ofsignal proportional to velocity (1) the average distance travelled bythe particles in a predetermined time or (2) the average time requiredfor the particles to travel a predetermined distance. The equations forcalculating Z? in these two cases are as follows:

ZP=K (d/V)(l.45 0.02t (I) where d is the average distance travelled andthe predetermined time is included in the constant K ZP=(-K /TV)(l.450.02t (2) where T is the average time required for the particles totravel. The predetermined distance is included in the constant KDETERMINING THE PROPER SET POINT ZETA POTENTIAL FOR OPTIMUMAGGLOMERATION Most suspensions of particles that are to be agglomeratedfor settling or flotation have an average Zeta Potential of 25 to 50millivolts. This means that there is a fairly strong negative charge oneach individual particle that repels any other approaching particles. Ithas been found that when the Zeta Potential is less than 20mv, there isa much stronger tendency for particles to agglomerate. When the ZetaPotential of a suspension is between -I 0 and 15 mv, the suspension issaid to be at the threshold of agglomeration, but its tendency toagglomerate depends on the individual suspension properties and the typeof agitation given to it. The actual Zeta Potential at whichagglomeration begins, if this indeed occurs at a sharp point, must bedetermined empirically for each suspension. Strong agglomeration andprecipitation occur in the Zeta Potential range of 5 to +5 mv. As theZeta Potential increases in the positive direction, the repelling forcesagain increase and the tendency to agglomerate drops off.

The average charge on the particles is a function of the surfaceproperties of the particle material and the amount and type of dissolvedsubstances in the suspension, and it is the result of preferentialadsorption of anions around the solid particles and solvation of cationsby the water molecules.

Most commonly used flocculents owe their effectiveness to their abilityto alter the charge on suspended particles by adding a surplus ofpositively charged cations to the suspension. The positive chargesneutralize the existing negative charges and cause the Zeta Potential toapproach zero. However, in most cases, it is a waste of flocculent tobring the Zeta Potential to zero. Some of the best known flocculents arecompounds containing ferric ions such as FeCl compounds containingaluminum ions such as AI SO.) and AICI and various cationicpolyelectrolytes such as Dow Purifloc C31 and Rohm and Haas C7.

With automatic and continuous monitoring of Zeta Potential and controlof the rate of flocculent addition based on a set point Zeta Potential,the minimum amount of flocculent is consumed to achieve the maximumbenefit. In general, the set point for agglomeration control is -11 mv,but this is flexible to allow for unusual conditions.

What is claimed is:

1. A method for determining the Zeta Potential of suspended colloidalparticles comprising the steps of:

a. establishing a predetermined voltage gradient along anelectrophoresis cell positioned on a microscope stage,

b. introducing a sample of said suspended colloidal particles into saidcell,

c. scanning a microscopic image of said colloidal particles within saidcell,

d. tracking said particles to determine their movement,

e. storing data representative of said particle movement;

f. calculating the particle velocity from said data, and

g. determining the Zeta potential from said particle velocity, thevoltage gradient of said cell, and the temperature of said suspendedcolloidal particles sample.

2. A method as in claim 1 wherein said particle velocity is determinedfrom the total distance travelled by the individual particles anddividing said total distance by the number of particles observed duringa fixed observation period.

3. The method as in claim 1 wherein said particle velocity is determinedby differentiating a signal representative of said particle displacementwith respect to time to provide a signal proportional to the rate ofchange of particle displacement.

4. A method as in claim 1 wherein the Zeta Potential is determined fromthe following formula: ZP -K, (V /V) (1.45 0.02t and wherein K 41rLn/D,

V is the electrophoretic velocity of said particles,

V is the voltage across said cell, t is the temperature of said sample,L is the length of said cell, D is the dielectric constant of saidsample, and n is the viscosity of said sample.

5. A method as in claim 1 wherein the Zeta Potential is determined fromthe following formula:

ZP =K (d/V) (1.45 0.022,.) wherein K 41rLn/D, d is the distancetravelled during a predetermined observation interval, V is the voltageof said cell, t is the temperature of said sample, L is the length ofsaid cell, n is the viscosity of said sample and D is the dielectricconstant of said sample and where K includes said predeterminedobservation interval.

6. A method as in claim 1 wherein the Zeta Potential is determined fromthe following formula: ZP (K /TV) (1.45 0.02t wherein K 41rLn/D, T isthe average time required for the particles to travel a predetermineddistance, V is the voltage across said cell, and t, is the temperatureof said sample, L is the length of said cell, n is the viscosity of saidsample and D is the dielectric constant of said sample and wherein Kincludes said predetermined distance.

1. A method for determining the Zeta Potential of suspended colloidalparticles comprising the steps of: a. establishing a predeterminedvoltage gradient along an electrophoresis cell positioned on amicroscope stage, b. introducing a sample of said suspended colloidalparticles into said cell, c. scanning a microscopic image of saidcolloidal particles within said cell, d. tracking said particles todetermine their movement, e. storing data representative of saidparticle movement; f. calculating the particle velocity from said data,and g. determining the Zeta potential from said particle velocity, thevoltage gradient of said cell, and the temperature of said suspendedcolloidal particles sample.
 2. A method as in claim 1 wherein saidparticle velocity is determined from the total distance travelled by theindividual particles and dividing said total distance by the number ofparticles observed during a fixed observation period.
 3. The method asin claim 1 wherein said particle velocity is determined bydifferentiating a signal representative of said particLe displacementwith respect to time to provide a signal proportional to the rate ofchange of particle displacement.
 4. A method as in claim 1 wherein theZeta Potential is determined from the following formula: ZP -K1 (Ve/V)(1.45 - 0.02tc) and wherein K1 4 pi Ln/D, Ve is the electrophoreticvelocity of said particles, V is the voltage across said cell, tc is thetemperature of said sample, L is the length of said cell, D is thedielectric constant of said sample, and n is the viscosity of saidsample.
 5. A method as in claim 1 wherein the Zeta Potential isdetermined from the following formula: ZP -K2 (d/V) (1.45 - 0.02tc)wherein K2 4 pi Ln/D, d is the distance travelled during a predeterminedobservation interval, V is the voltage of said cell, tc is thetemperature of said sample, L is the length of said cell, n is theviscosity of said sample and D is the dielectric constant of said sampleand where K2 includes said predetermined observation interval.
 6. Amethod as in claim 1 wherein the Zeta Potential is determined from thefollowing formula: ZP (K3/TV) (1.45 - 0.02tc) wherein -K3 4 pi Ln/D, Tis the average time required for the particles to travel a predetermineddistance, V is the voltage across said cell, and tc is the temperatureof said sample, L is the length of said cell, n is the viscosity of saidsample and D is the dielectric constant of said sample and wherein K3includes said predetermined distance.